This invention has application in those installations where one or more tanks, hereafter denoted as "tank means," are employed for the storage of volatile liquids; i.e., those which exhibit a vapor pressure such that at least a partial vapor fraction is present within the tank simultaneously with the liquid fraction. In practice, such installations will commonly include not only transportation vessels such as barges, railroad cars, tank trucks and the like; but also fixed installations for the storage of such liquids. In the operation of these installations, a problem exists in that it is undesirable from an environmental point of view for waste gas from these tank means to be discharged to the atmosphere, a situation which has been recognized by the Environmental Protection Agency as evidenced by its regulations governing such discharges.
The use of an incinerator for disposal of these waste gases is recognized as an adequate solution to this problem, although it must be equipped with control means such that a suitable operating temperature and a sufficient quantity of oxygen is maintained therein despite variations in quantity and heating value of the waste gas. This is necessary in order to assure proper disposal of the waste gas. Said control means must be adequate to modulate the flow of fuel, combustion air, incineration air, and waste gas to the incinerator throughout its operating range.
Associated with the aforementioned problem of waste gas disposal is the requirement that these tank means be washed down on a periodic basis, usually before refilling, and that an inert purge gas be applied thereto in order to assure that an explosive mixture of waste gas and oxygen is not present therein.
It is thus desirable that an installation of the type described be equipped with means for disposal of waste gas from the tank means and for washing down and purging same.